The general aim of this research is to provide information about the development mechanisms responsible for the specificity of the synaptic connections formed by primary sensory neurons in the spinal cord during embryonic development and to gain insight into factors that might promote regeneration of functionally appropriate connections following injury. Developing sensory neurons innervate peripheral targets before they form central connections and it has been suggested that the central connections of sensory neurons actually are determined by their peripheral targets. This hypothesis was tested by forcing sensory neurons in bullfrog tadpoles to innervate a foreign peripheral target and then examining the central connections of these neurons by anatomical and electrophysiological methods. The results support the suggestion that central connections of sensory neurons are influenced by their targets but also suggest that they depend on the axial level at which the central processes enter the spinal cord and on the presence or absence of ganglia in adjacent segments. The formation of appropriate connections by sensory neurons requires that they develop terminal arbors in specific areas of the spinal cord- in order to identify the environmental cues that guide sensory axons and that induce them to form branches, we are using videomicroscopy to determine how the branching patterns of neurons growth in vitro are influenced by contacts with other cells, purified substrate molecules and growth factors. Our initial studies have focused on early stages in axon outgrowth and the establishment of neuronal polarity.